Various systems for the hydrolysis of urea are known in the art. Technology currently employed in the U.S. is summarized by the EPA report Number 440/1-73/011, Development Document for Proposed Effluent Limitations Guidelines and New Source Performance Standards for the Basic Fertilizer Chemicals Segment of the Fertilizer Manufacturing Point Source Category. The urea hydrolysis systems practiced normally entail the use of a plurality of trays in a column. The urea waste stream is fed to the top of the column and a counter-current stream of steam is fed from the bottom. Although any free ammonia found in this stream is removed, a substantial amount of the urea passes through the column and into the effluent stream. Urea is considered deleterious in natural waterways in that it promotes algae growth and hydrolyzes slowly, releasing ammonia which is toxic to fish.
This invention provides for the destruction of the urea by hydrolyzing, forming volatile ammonia and carbon dioxide. These products are then removed by stripping performed in the hydrolysis column.
My co-pending application Ser. No. 609,475 filed Sept. 22, 1976 now abandoned, discloses the use of liquid holding zones within a vessel to improve the urea hydrolysis. The present invention improves on this concept by combining the stripping and hydrolysis functions into one or more treating cells. This improvement greatly reduces the size and cost of the vessel needed for this process, particularly where requirements are for a high degree of urea removal efficiency.